Thermorelay with indirectly heated bimetallic strip



A. VIBOUD x Sept. 1, 1953 THERMORELAY WITH INDIRECTLY HEATED BIMETALLIC STRIP Filed March 14, 1952 Invento r' B 6 n m 1%.. r e n A Patented Sept. 1, 1953 THERMORELAY WITH INDIRECTLY HEATED BIMETALLIC STRIP Albert Viboud, Grenoble, France, assignor to Etablissements Merlin & Gerin, Societe Anonyme, Grenoble, France, a corporation of France Application March 14, 1952, Serial No. 276,720 In France April 4, 1951 4 Claims.

The invention is concerned with a thermorelay of the type in which the bimetallic strip of a thermostat is indirectly heated by a heating element disposed in close proximity to the bimetallic strip.

In thermorelays of this type the current flows through the heating element and the joule heat generated thereby is radiated or otherwise transmitted to the bimetallic strip adjacent thereto which, owing to the difiering coeflicients of expansion of the two metals of which the strip is composed, will be curved or deflected, the extent of the curvature or deflection being dependent upon the intensity of the current which flows through the heating element.

An object of the invention is a development of a thermorelay in which the distribution of the heat supplied by the heating element may readily and precisely be predetermined, viz., the proportion between useful heat transmitted to the bimetallic strip and lost or dispersed heat, and thus the extent to which the bimetallic strip is deflected.

A further object of the invention is the overcoming in such apparatus of the difficulty that for a given bimetallic strip the temperature defiection characteristic is fixed and thus the heattime characteristic or the timing of the relay.

However, it is often desirable to accelerate or to delay the actuation of the strip or to modify any part of its deflecting motion. Merely resetting the one or the other of the terminals of the strip does not change the course proper of its deflection-time curve but extends or shortens this curve without changing its character.

The inventor now has discovered that it is possible to change the character of this timedefiection relationship, thus to accelerate or to delay any part of the strip deflection and thus, for instance, to provide for a more rapid or for a slower closing or opening of the switch, if so desired.

It is thus an object of the invention to modify the time-heat characteristic of the relay, not by changes at the bimetallic strip itself, but by modifying or controlling or regulating, dependent upon the motion of the bimetallic strip, the thermic conditions of the space, wherein the heat for the indirect heating of the bimetallic strip is transmitted from heating element to strip,

thus by utilizing the condition that the operation of the relay, in addition to the temperature deflection-characteristic of the strip, depends upon the heat transmission capacity of the comomn environment of strip and heating element or of the space wherein they are arranged in more or less close vicinity to each other.

An object of the invention thus is a temperature control device which makes possible the regulation and control at will of the time-temperature characteristic of the relay thus the precise control of the time delay when, as soon as a given current intensity is reached, the relay mechanism is to be released and the velocity with which it is to be released and thereafter to be reset.

The invention will be more specifically described hereinafter in its application to a bimetallic strip wound as a helix.

Through this arrangement, the convolutions 01' the helix, when the bimetallic strip is heated, will lengthen and displace themselves peripherally within the curved surface of the cylinder which envelops the coil, without noticeable change of the diameter of the coil or helix. The free end of the helix, the other end being fixed, will be displaced along a helical line around this cylinder surface.

In this thermorelay with a bimetallic strip wound as a helix, the switching means of the relay are coupled with this helix for operating the relay dependent upon the thermic conditions to which the helix is subjected. The relay is provided with the conventional terminals which are to be connected to the electrical circuit in which the relay is operative.

Between these terminals, the heating element is electrically inserted. The current of the relay circuit thus passes through and heats the heating element which, for its part, is disposed in vicinity to the helix. The heat is thus transmitted to the helix which in this way is indirectly heated by the current of the relay circuit.

The heating element may be disposed within the generating cylinder of the helix, axially extended therein, coaxially with the helix, such as in the form of a rod, a wire, or a wire wound as a coil, or in the form of a cylinder, or in any other convenient form or shape.

Both bimetallic helix and heating element are enclosed in a casing, preferably cylindrical.

Since bimetallic helix and heating element are lodged within a closed space, the control of the released thermic energy is made possible, as will be set forth hereinafter in detail.

The arrangement of a closed casing, preferably extended in the vertical direction, allows this casing to function as a kind of flue if there is provided one or more openings through which the heated air may escape from the heated interior of the enclosure, In order to control, regulate, or modify the thermic conditions of the space within the casing, the velocity of the circulation of this air may be controlled by the varia tion of the section of the openings, for instance by means of a register. A rapid return of the bimetallic strip into zero position may thus be achieved and, concomitantly, the possibility of controlling the relay, conformably to a given thermic image closely approximating that of the apparatus to be protected.

For further illustration of these and other objects and features of the invention, reference will now be made to the accompanying drawings which form part of this specification and which are to be understood explicative of the invention but not limitative of its scope.

The drawings thus are to show an embodiment of the invention but not to limit the scope of my invention through or to the particularities of the example selected for illustration. Other embodiments incorporating the principles underlying my invention are feasible without departing from the spirit and ambit of my appended claims.

In the drawings:

Fig. l is an elevational view of an embodiment of the thermorelay of the invention;

Fig. 2 is a diagrammatic perspective of a switch release mechanism controlled by the thermorelay of Fig. 1;

Fig. 3 illustrates, likewise in diagrammatic perspective, a control mechanism of a ventilating device for the bimetallic helix of Fig. 1.

In the drawings, I l and I2 are the terminals of the relay. Electrically connected with these terminals is the heating element, in the embodiment of Fig. 1 in the form of an exchangeable rod E3 of any convenient or conventional conductive or semiconductive material.

The rod is secured directly to the upper terminal ii and to the lower terminal 12 through the intermediary of an expansion compensator M. The bimetallic strip of conventional material is wound as a helix l5 coaxially with the rod.

The upper terminal or head piece ll carries, suspended therefrom, a cylindrical casing 20 of any appropriate material, metal or heat resisting insulating material ever according to the desired working characteristics of the thermorelay. The helix with its one end it is secured to the casing near the upper end thereof and is thus suspended within the cylindrical casing coaxially therewith and also coaxially with the heating element, or rod I3.

The cylindrical casing 20 is open at both its ends. The upper end, however, is covered by the terminal or head piece which in this embodiment of the invention is pierced by one or more ventilation ducts iii and i9. These ventilation ducts may open at the upper face of the terminal H, as illustrated, but may also be arranged otherwise such as to open at the side faces of the terminal. In accordance with this development of the invention the passage through these ducts may be regulated and controlled thus by being opened or closed more or less by an appropriate arrangement, for example by a register 23, the arrangement and function of which will be described later on.

The device operates as follows:

As long as the rod i3 is traversed by the normal current it releases only weak heat which does not suiiice to deflect the free end of the helicoidal bimetallic strip to an appreciable extent since this heat is carried off through the ducts I8 and [9 by the air current which the heat creates.

As soon as the electric current reaches a predetermined intensity the excess of heat produced by the heating element [3 causes the free end ll of the bimetallic helix to actuate the release mechanism of the switch.

An embodiment of such a release mechanism operated by the bimetallic helix is shown in Fig. 2.

The free end I? of the helix bears against the end l! of a pin 4%? slidably mounted in the support 63. This pin is held in its normal rest position by a spring l ibearing at its one end against the support 4'3 and with its other end against a shoulder' i5 of the pin. The pin 4!) when pushed rearwards by the free end ll of the bimetallic helix I5 will bear with its end 42 against and rock a vane it, oscillatable about its rock shaft ll, and so suspended upon this shaft that the center of gravity is below the rocking axis, so that when the pin ill is withdrawn by the action of the spring into its normal rest position, the vane 65 will return into its vertical rest position. The switching contacts are and 5|. Contact 5! is stationary whereas contact 5%] is carried by a rockable crank lever 53 with rock shaft 5'3. The free end 5-5 of the crank lever in the closed position of the switch bears under the pull of a spring 55 upon vane 26.

When the bimetallic helix is heated, its free end ll will push pin it in the direction of the arrow A against the tension of spring M. As soon as the free end B? of the helix has been sufficiently displaced and the spring it correspondingly compressed, pin til will push against vane d6 and rock it in the sense of arrow B. Lever 53 is thus released and contact 56) under the action of spring 55 will leave the stationary, fixed contact 5|, and the circuit will thus be opened.

If later on the circuit is again to be closed, the contact may be reset by any conventional means, here not described since these means do not form part of this invention.

Since the bimetallic helix heats up only gradually and it is desirable that the circuit breaker opens only after certain delay and at a predetermined overload, the mechanism is so designed that the end I! of the helix l5 may already bear against the pin ii! before the point of overcharge is reached at which the switch is to open.

The spring 4d therefore is so designed that the pin All will rock the vane 36 and thus trip contact 5| at the precise moment when the overload is reached at which the relay is to operate.

For further control of the sensitivity of the relay, the passage through the ventilation ducts E8, 19, in accordance with the invention, is governed by a register 23 controlled by the displacement of the free end ll of the helix l5.

Fig. 3 shows schematically an embodiment of such a governing and control device.

The ventilation ducts l8 and it which traverse the terminal I I, end in ports 2i and 22 the passage through which may be more or less obstructed or choked by the narrowing or tapering openings 24, 25, respectively, of the register 23. This register is provided with. a finger 265 which is engaged by the forked end 2'5 of a reel; lever 28 oscillatorily supported by a rock shaft 30. The other end 29 of rock lever 28 is likewise forked and engages the free end i! of the bimetallic helix.

As soon as the bimetallic strip heats up sufficiently and its end I! is displaced in the sense of the arrow A, the same sense as indicated in Fig. 2, end ll rocks the lever 25 and pushes its end 27 in the direction of the arrow C. The register 23 will thus be rotated in the sense of arrow D about its axis 3|.

The openings 24 and 25 of the register will thus increasingly obstruct or choke the ports 2|, 22, respectively, of the ventilation ducts l8 and it through which the hot air within the casing 29 may escape into the free atmosphere. The circulation of the ventilation air will thus be choked or even impeded and the functioning of the apparatus accelerated.

This acceleration may be set to any desired degree by giving the leverage G/H the proper desired value. The greater this value, the faster will be the functioning of the bimetallic strip when it is heated, and conversely, the faster will be the cooling down of the helix when the overload has disappeared.

I claim:

1. Thermorelay with bimetallic strip and switching means coupled with said strip for operating the relay dependent upon the thermic condition of said strip, said relay having terminals adapted to be connected with the electrical circuit in which the relay is operative; a heating element electrically connected to and between said terminals so as to be passed by the current of said circuit and to be heated thereby; a casing disposed at said thermorelay; said bimetallic strip and said heating element being housed in the space of said casing and in vicinity to each other so as for said heating element to transmit heat to said strip for the indirect heating of the same; supplemental regulating mechanism being coupled with said strip so as to be actuated thereby and, dependent upon the deflection of the strip, to modify the thermic condition of the space thus the time-heat characteristics of the relay.

2. Thermorelay as set forth in claim 1 wherein said casing comprises ventilation apertures, a register for the control of said apertures; said mechanism being further coupled with said register, thereby, on deflection of said strip, to con- -3 trol the setting of the register and thus the passage of the ventilating air through said ventilation apertures.

3. Thermorelay with bimetallic strip in the shape of a helix and switching means coupled with said helix for operating the relay dependent upon the thermic condition of said helix, said relay further having terminals adapted to be connected with the electrical circuit in which the relay is operative; a heating element electrically connected to and between said terminals and adapted to be passed by the current of said circuit and to be heated thereby; said heating element disposed in vicinity to said helix so as to transmit heat thereto for indirect heating of said helix by said current; a casing disposed at said thermorelay, said helix and said heating element being enclosed in the space of said casing, supplemental regulating mechanism being provided at said relay and at said casing and coupled with said helix so as to be actuated thereby and, dependent upon the deflection of the strip, to modify thereby the thermic condition of the space enclosed Within said casing and thus the timeheat characteristic of the relay.

4. Thermorelay as set forth in claim 3 wherein ventilation apertures are provided in said casing for ventilating the space in said casing and a register is provided at said apertures, said helix having one of its ends fixed and the other end free, control mechanism being coupled with said free end of the helix and with said register thereby, on deflection of said free end of the helix, to control the setting of the register and thus the passage of the ventilating air through said ventilating ducts.

ALBERT VIBOUD.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,343,461 Ettinger et al Feb. 22, 1944 2,350,403 Kulka June 6, 1944 2,354,529 Ludwick July 25, 1944 2,411,352 Armstrong Nov. 19, 1946 

